In To Conserve Unimpaired, Professor Robert Keiter provides an unvarnished view of "America's best idea": the National Park System. Keiter, the country's pre-eminent legal expert on the subject, tackles the question: Why does the park idea still evoke so much controversy when its value is so widely acknowledged? For one thing, as he explains, it's not just about parks. "As highly valued and visible public places, the national parks are inherently political entities … reflecting our larger dialogue about nature conservation and its role in our civic life."

Keiter traces the evolution of each major idea that has shaped our vision of the national parks. In the early days, the Park Service actively sought to improve visitor experiences by attempting to control nature. Not only did the agency suppress wildfires, it also eradicated wolves to protect more "desirable" wildlife, and fed bears garbage "to create an evening spectacle for park visitors." If it weren't for David Brower and the Sierra Club, Dinosaur National Monument would have been inundated by the massive Echo Park dam. But they could not stop the Park Service from punching through a network of new roads to facilitate tourism. Brower captured the dichotomy of all national parks: "Part schoolroom and part playground and part – the best part – sanctuary from a world paved with concrete, jet-propelled, smog-blanketed, sterilized, over-insured, (and) aseptic … with every natural beautiful thing endangered by the raw engineering power of the twentieth century."

The challenge of conserving those "beautiful things" looms even larger today, as we face the pressures of climate change and ever more people and development. One can't help but wonder whether the legal mandate governing park management, the Organic Act of 1916, is adaptable enough to endure. In fact, the Park Service's management ethos did begin to change in the 1960s with the influential Leopold report – by legendary conservationist Aldo Leopold – which recommended that parks be managed to represent a "vignette of primitive America" with minimal human intervention into natural processes.

Keiter shows how the Organic Act can continue to accommodate changing views of the national parks while ensuring that conservation comes first. He points the way toward conserving the parks "unimpaired for the enjoyment of future generations," as the law specifies, through science, collaboration, and a heightened sense of social justice, connectivity, and diversity, both human and ecological. Yet, as Keiter concludes, "The parks will always be confronted with new demands and threats, testing our commitment to the fundamental principles underlying the hallowed notion of conserving nature in an unimpaired condition."

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The Leopold Report of 1963 did indeed play a major and long-lasting role in the evolution of Park Service thinking, and it strongly influenced policy and management. However, it was not written by Aldo Leopold (who died in 1948), but rather by a committee of esteemed wildlife biologists chaired by A. Starker Leopold, Aldo's son. Addressing a conference of western NPS superintendents about a decade later, Leopold said that he regretted the memorable "vignette" statement, because it implied a static nature, when in fact nature is dynamic in the face of ever-changing physical and biological forces. Today, the National Park Service faces its greatest challenge in climate change. Park landscapes will undergo profound change. The Organic Act and NPS policies may well be able to accommodate these changes, but that begs the question: What should parks be attempting to manage for under constantly changing conditions?